ROLE OF THE SYMPATHETIC SYSTEM IN REFLEX DILATATION OF PUPIL

Abstract

The role of para-sympathetic inhibition and that of sympathetic excitation in reflex pupillary dilatation in cats (with and without ether narcosis) was analyzed by recording photographically the pupillary changes in the normal, the parasympathectomized, and in the sympathectomized eye. After section of the 3d nerve and local application of eserine, the threshold of the cephalad end of the cervical sympathetic remained unchanged; indicating that such a pupil might be used as an indicator of sympathetic impulses. On reflex stimulation which evoked struggle and vocalization the parasympathectomized pupil remained unchanged or showed a very slight dilatation (not more than 1 mm.), whereas the normal pupil dilated 7 mm. After sensitiza-tion with subconvulsive concentrations of metrazol the sympathetic reflex response of the pupil increased. During metrazol convulsions the parasympathectomized and eserin-ized pupil dilated to 7 or 8 mm. Under normal conditions the pupillary dilatation in response to pain was almost exclusively due to parasympathetic inhibition but under conditions which increased the excitability of the cilio-spinal center (metrazol), sympathetic discharges probably contributed materially to the dilatation.